This invention relates to an expansion device and a refrigerant cycle wherein the expansion device does not lower the pressure of a refrigerant at low charge condition as much as it does under normal operation.
Refrigerant cycles are utilized for cooling purposes. As an example, refrigerant cycles are incorporated into air conditioning and refrigeration systems. In a refrigerant cycle a refrigerant passes from a compressor to a condenser. The refrigerant is compressed in the compressor, and gives off heat to the environment in the condenser. From the condenser, the refrigerant passes to an expansion device. At the expansion device, the pressure of the refrigerant is significantly reduced. Typically, the refrigerant is passed through an orifice to expand and reduce its pressure. From the expansion device, the refrigerant passes to an evaporator. In the evaporator, the refrigerant cools an environment to be cooled by the refrigerant system. The refrigerant returns to the compressor from the evaporator. This is a somewhat simplified explanation, and many other components are often incorporated into the refrigerant cycle. However, this basic description does accurately reflect the operation of refrigerant cycle.
Typically, the connections and various components in the refrigerant cycle are sealed such that the refrigerant does not leak. However, in practice, refrigerant does sometimes leak outwardly of the system. When leaks occur, the charge of refrigerant is decreased from that which is desirable. When there is a lower charge refrigerant than is desirable, operation of the compressor becomes somewhat complicated. Low refrigerant charge may result in abnormally low suction port pressures. When this low pressure vapor is compressed to the relatively high discharge pressure, the resulting high pressure ratio compression process causes high discharge temperatures in the compressor. This is undesirable.
In one particularly popular modern compressor, two scroll members orbit relative to each other to compress refrigerant. The high pressure ratios as described above under low charge operation are particularly undesirable in a scroll compressor.
In a disclosed embodiment of this invention, a compressor in a refrigerant cycle is protected during low charge operation by modifying the expansion device such that it does not lower the pressure as much when low charge operation is sensed. The expansion device will normally lower the pressure to a first relatively low pressure. However, if the system senses that there is a low charge, then the expansion device does not lower the pressure to the first low pressure. That is, the expansion device operates in both a normal and a low charge mode.
In one embodiment, the expansion device is provided with a bypass line. The bypass line can be inserted internally into the expansion valve body, or can be an external connection. However, for purposes of this application, a bypass line which bypasses from a downstream location relative to the condenser to an upstream location relative to the evaporator will be considered as part of the expansion valve. In normal condition, the bypass line is closed. However, if a loss of charge situation is identified due to conditions within the refrigerant cycle, the bypass is open. In this way, the refrigerant is not brought to the lower pressure in the expansion device. Thus, the refrigerant delivered to the suction side of the compressor will be at a higher pressure than it would have been in the prior art. The pressure ratio across the compressor will thus not be as high in a low charge situation as is the case in the prior art.
In the second embodiment, the expansion device includes a piston which is driven between normal and low charge positions. In the normal position, the valve provides a restriction to flow that will result in the reduced pressure. However, in the loss of charge condition, the piston will present less of a restriction to flow, and the pressure will thus not be as lower, providing a similar effect as in the prior embodiment.
The identification of a low charge situation is specifically disclosed by monitoring the inlet and discharge pressure to the compressor. However, other methods of identifying a low charge situation can be utilized. A worker in this art would recognize several ways of identifying such a condition.
These and other features of the present invention can be best understood from the following specification and drawings, the following of which is a brief description.